This is an overview of the fossil flora and fauna of the Maastrichtian-Danian Hell Creek Formation.
Invertebrates
Insects Insects from the groups Diptera, Zygoptera, and possibly Hemiphlebiidae have been unearthed in Hell Creek in amber. Fossils found in the Hell Creek Formation and the Fort Union Formation of these insects went extinct during the K-T Event.
Molluscs
Amphibians
Fish
Bony fish
Cartilaginous fish
Dinosaurs A paleo-population study is one of the most difficult of analyses to conduct in field paleontology. Here is the most recent estimate of the proportions of the eight most common dinosaurian families in the Hell Creek Formation, based on detailed field studies by White, Fastovsky and Sheehan.
Ceratopsidae 61% Hadrosauridae 23% Ornithomimidae 5% Tyrannosauridae 4% Hypsilophodontidae 3% Dromaeosauridae 2% Pachycephalosauridae 1% Ankylosauridae 1% Troodontidae 1% (represented only by teeth)
Outcrops sampled by the Hell Creek Project were divided into three sections: lower, middle and upper slices. The top and bottom sections were the focus of the PLoS One report, and within each portion many remains of Triceratops, Edmontosaurus, and Tyrannosaurus were found. Triceratops was the most common in each section, but, surprisingly, Tyrannosaurus was just as common, if not slightly more common, than the hadrosaur Edmontosaurus. In the upper Hell Creek section, for example, the census included twenty two Triceratops, five Tyrannosaurus, and five Edmontosaurus. The dinosaurs Thescelosaurus, Ornithomimus, Pachycephalosaurus and Ankylosaurus were also included in the breakdown, but were relatively rare. Other dinosaurs, such as Sphaerotholus, Denversaurus, Torosaurus, Struthiomimus, Acheroraptor, Dakotaraptor, Pectinodon, Richardoestesia, Paronychodon, Anzu, Leptorhynchos and Troodon (more likely Pectinodon), were reported as being rare and are not included in the breakdown. The dinosaur collections made over the past decade during the Hell Creek Project yielded new information from an improved genus-level collecting schema and robust data set that revealed relative dinosaur abundances that were unexpected, and ontogenetic age classes previously considered rare. We recognize a much higher percentage of Tyrannosaurus than previous surveys. Tyrannosaurus equals Edmontosaurus in U3 and in L3 comprises a greater percentage of the large dinosaur fauna as the second-most abundant taxon after Triceratops, followed by Edmontosaurus. This is surprisingly consistent in (1) the two major lag deposits (MOR loc. HC-530 and HC-312) in the Apex sandstone and Jen-rex sand where individual bones were counted and (2) in two thirds of the formation reflected in L3 and U3 records of dinosaur skeletons only. Triceratops is by far the most common dinosaur at 40% (n = 72), Tyrannosaurus is second at 24% (n = 44), Edmontosaurus is third at 20% (n = 36), followed by Thescelosaurus at 8% (n = 15), Ornithomimus at 5% (n = 9), and Pachycephalosaurus and Ankylosaurus both at 1% (n = 2) are relatively rare. Fossil footprints of dinosaurs from the Hell Creek Formation are very rare. As of 2017, there is only one find of a possible Tyrannosaurus rex footprint, dating from 2007 and described a year later. A trackway made by mid-sized theropod, possibly a small tyrannosaurid individual, was discovered in South Dakota in 1997, and in 2014 these footprints were named Wakinyantanka styxi.
Ornithischians
Ankylosaurs Indeterminate nodosaur remains have been unearthed in the Hell Creek Formation and other nearby areas.
Pachycephalosaurs An undescribed and unnamed pachycephalosaur is present in North Dakota. Pachycephalosaur remains have been unearthed in Montana as in the case of Platytholus and the now invalid genus Stenotholus kohleri, which is now a junior synonym of Pachycephalosaurus. Dracorex hogwartsia is agreed by paleontologists to be an ontogimorph of either Pachycephalosaurus or Stygimoloch, while the synonymy of Stygimoloch spinifer with Pachycephalosaurus wyomingensis remains uncertain due to difference in stratigraphic level.
Ceratopsians Indeterminate ceratopsid teeth and some identifiable bones from Triceratops can be extremely common. 8.31% of all vertebrate remains from the Hell Creek Formation are unassigned ceratopsids, as well as dubious ceratopsians like Ugrosaurus olsoni. In 2012, a new unidentified species of chasmosaur ceratopsian with noticeable differences from Triceratops was unearthed in South Dakota by a fossil hunter named John Carter.
Ornithopods and relatives Indeterminate hadrosaurid remains are very common in the Hell Creek Formation. Fossils of indeterminate lambeosaurs have been unearthed in Hell Creek, specifically in South Dakota and Montana.
Theropods Theropod tracks have been found in South Dakota. A trackway from South Dakota, named Wakinyantanka, was made by a mid-sized theropod with three slender toes, possibly a small tyrannosauroid or oviraptorosaur. A second footprint that may have been made by a specimen of Tyrannosaurus was first reported in 2007 by British paleontologist Phil Manning, from the Hell Creek Formation of Montana. This second track measures 72 centimeters (28 in) long, shorter than the track described by Lockley and Hunt. Whether or not the track was made by Tyrannosaurus is unclear, though Tyrannosaurus is the only large theropod known to have existed in the Hell Creek Formation; albertosaurine remains have been reported but are misattributed Tyrannosaurus or Nanotyrannus. Theropod remains are very common in Hell Creek, some of which belong to indeterminate species on maniraptorans. Indeterminate and dubious tyrannosaur fossils are found here as in the case of Stygivenator.
Alvarezsaurs
Tyrannosauroids
Ornithomimosaurs Ornithomimid remains are not uncommon in the Hell Creek Formation, and are known from both the lower and upper parts of the formation. Fifteen specimens from the Hell Creek Formation are undetermined ornithomimids.
Oviraptorosaurs Oviraptorosaur fossils have been found at the Hell Creek Formation for many years, most notably from isolated elements until the discovery of Anzu. In the past, oviraptorosaur fossils found were thought to have belonged to Leptorhynchos, Caenagnathus, Chirostenotes, and Elmisaurus. In 2021, a large-bodied caenagnathid specimen (ROM VP 65884) from Montana was referred to cf. Anzu wyliei.
Eumaniraptorans Historically, numerous teeth have been attributed to various dromaeosaurid and troodontid taxa with known body fossils from only older formations, including Saurornithoides, Zapsalis, Dromaeosaurus, Saurornitholestes, and Troodon. However, in a 2013 study, Evans et al. concluded that there is little evidence for more than a single dromaeosaurid taxon, Acheroraptor, in the Hell Creek-Lance assemblages, which would render these taxa invalid for this formation. This was seemingly disproven in 2015, when DePalma et al., described the new genus Dakotaraptor, a large species of dromaeosaur. However, Dakotaraptor's validity has been called into question since, as the holotype may be a chimeric assemblage of various non-dromaeosaurid coelurosaurians. Fossilized teeth of various troodontids and coelurosaurs are common throughout the Hell Creek Formation; the best known examples include Paronychodon, Pectinodon and Richardoestesia, respectively. Teeth belonging to possible intermediate species of Dromaeosaurus and Saurornitholestes have been unearthed at the Hell Creek Formation and the nearby Lance Formation.
Pterosaurs Undescribed pterosaur remains were reported from North Dakota. Undescribed pteranodontian specimen has also been mentioned in the supplementary material of Longrich et al. (2018).
Crocodylomorphs
Turtles
Squamata
Choristoderans
Mammals
Multituberculates
Metatherians
Eutherians
Flora The Hell Creek Formation was a low floodplain at the time before the sea retreated, and in the wet ground of the dense woodland, the diversity of angiosperms and conifers were present. A diversity of herbaceous flowering plants, ferns and moss grew in the forest understory. On the exposed point bars of large river systems, there were shrubs and vines. The evidence of the forested environment is supported by petrified wood, rooted gley paleosols, and ubiquitous tree leaves. The presence of the simple and lobed leaves, combined with a high dicot diversity, extinct cycadeoid Nilssoniocladus, Ginkgo, many types of monocots, and several types of conifers is different from any modern plant community. There are numerous types of leaves, seeds, flowers and other structures from Angiosperms, or flowering plants. The Hell Creek Formation of this layer contains over 300 tablets, of which angiosperms are the most diverse and dominant flora of the population, about 90 percent, followed by about 5% of conifers, 4% of ferns, and others. Compared to today Hell Creek's flora which is prairie, then Hell Creek's flora was hardwood forest mixed with deciduous and evergreen forest. In sharp contrast to the Great Plains today, the presence of some thermophilous taxa such as palm trees and gingers meant the climate was warmer and wetter then.
The plants of the Hell Creek Formation generally represent angiosperm-dominated riparian forests of variable diversity, depending on stratigraphic position and sedimentary environment. There appears to be floral transitions visible on a stratigraphic range from the lower to the upper Hell Creek Formation. For this reason, Kirk Johnson and Leo Hickey divided it into five zones and described them as HCIa, HCIb, HCIIa, HCIIb, and HCIII as a reflection of floral change through time. For example, the HCIa zone is dominated by "Dryophyllum" subfalcatum, Leepierceia preartocarpoides, "Vitis" stantonii, and "Celastrus" taurenensis, and is located 55 to 105 meters below the K-Pg boundary layer. Although the HCIb zone is a very thin layer, about 5 meters of rock, it bears unusually high diversity of herbaceous and shrubby plants, including Urticaceae, Ranunculaceae, Rosaceae, and Cannabaceae.
There is evidence of transitional floras in the middle of the Hell Creek Formation as shown by HCII and HCIII zones. The HCII flora represents a transitional period where taxa from the lower Hell Creek are replaced by the HCIII flora. The diversity of the HCIII zone is very high, and its composition is more uniform than that of HCII, many of which were rare or absent from the zones below, and some others that used to be common below became rarer in the HCIII zone. These forms include Elatides longifolia, "Dryophyllum" tennessensis, Liriodendrites bradacii, and many members of the Laurales including Bisonia niemii, "Ficus" planicostata, and Marmarthia trivialis, while "Celastrus" taurenensis, Leepierceia preartocarpoides, and many cupressaceous conifers became rarer. This phenomenon suggests that the global temperature was warming during the last 300,000-500,000 years of the Cretaceous period. There is no evidence of fern prairie in the Hell Creek Formation. However, there was high angiosperm diversity — common plane trees, "Dryophyllum" subfalcatum, Leepierceia preartocarpoides, and sabal palms — along with extinct cycadeoid Nilssoniocladus, Ginkgo, araucariaceous, Taxodiaceous, and cupressaceous conifers. This represents the mixed deciduous and evergreen broad-leaved forest of the Hell Creek landscape. The nature of these forests is uncertain because Johnson found that the majority of the angiosperm and conifer genera are now extinct. He also believes that, very roughly 80% of the terrestrial plant taxa died out in what is now Great Plains at the K-Pg boundary. On other hand, there is a great increase in the abundance of fossil fern spores in the two centimeters of rock that directly overlies the impact fallout layer (the famous K-Pg boundary layer). This increase in fern spore abundance is commonly referred as "the fern spike" (meaning that if the abundance of spores as a function of stratigraphic position were plotted out, the graph would show a spike just above the impact fallout layer). Many of the modern plant affinities in the Hell Creek Formation (e.g., those with the prefix "aff." or with quotes around the genus name) may not in reality belong to these genera; instead they could be entirely different plants that resemble modern genera. Therefore, there is some question regarding whether the modern Ficus or Juglans, as two examples, actually lived in the Late Cretaceous. Compared to the rich Hell Creek Formation fossil plant localities of the Dakotas, relatively few plant specimens have been collected from Montana. A few taxa were collected at Brownie Butte Montana by Shoemaker, but most plants were collected from North Dakota (Slope County) and from South Dakota. Among the localities, the Mud Buttes, located in Bowman County, North Dakota, is probably the richest megaflora assemblage known and the most diverse leaf quarry from the Hell Creek Formation. "TYPE" after the binomial means that it is represented by a type specimen found in the Yale-Peabody Museum collections. "YPM" is the prefix for the Yale-Peabody Museum specimen number; "DMNH" is for the Denver Museum of Nature & Science; "USNM" is for Smithsonian National Museum of Natural History; and so on. The majority of Hell Creek megafloral specimens are collected at the Denver Museum of Nature & Science.
Overview (from Johnson, 2002) 302 plant morphotypes based on leaf only, including:
1 bryophyte (mosses and liverworts) 11 ferns 1 sphenopsid 10 conifers 1 ginkgo (uncommon) 278 angiosperms (roughly 92% of all taxa found)
Paleoflora
Liverworts
Ferns
Cycadophytes
Ginkgoales
Conifers
Angiosperms
Palynology
See also List of fossil sites (with link directory) Lists of dinosaur-bearing stratigraphic units Paleobiota of the Morrison Formation Lance fauna Cretaceous-Paleogene formations Tremp Formation, Spain Tremp Formation, Spain Lefipán Formation, Argentina López de Bertodano Formation, Antarctica
References
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(2013), "A new dromaeosaurid (Dinosauria: Theropoda) with Asian affinities from the latest Cretaceous of North America", Naturwissenschaften, 100 (11): 1041–1049, Bibcode:2013NW....100.1041E, doi:10.1007/s00114-013-1107-5, PMID 24248432 Bibcode:2013NW....100.1041E Husson, D.; Galbrun, B.; Laskar, J.; Hinnov, L.A.; Thibault, N.; Gardin, S.; Locklair, R.E. (2011), "Astronomical calibration of the Maastrichtian (late Cretaceous)", Earth and Planetary Science Letters, 305 (3): 328–340, Bibcode:2011E&PSL.305..328H, doi:10.1016/j.epsl.2011.03.008 Bibcode:2011E&PSL.305..328H LeCain, Rebecca (2010), "Magnetostratigraphy of the Hell Creek and lower Fort Union formations in northeast Montana", Master's Theses and Capstones, p. 1, retrieved 2020-03-30 Johnson, K.R.; Nichols, D.J.; Hartman, J.H. (2002), "Hell Creek Formation: A 2001 synthesis. The Hell Creek Formation and the Cretaceous-Tertiary Boundary in the northern Great Plains", Geological Society of America Special Paper, 361: 503–510 Paleontology DePalma, Robert (2010), "Preliminary Notes on the First Recorded Amber Insects from the Hell Creek Formation", The Journal of Paleontological Sciences, retrieved 2019-02-21 Boyd, Clint A.; Brown, Caleb M.; Scheetz, Rodney D.; Clarke, Julia A. (2009), "Taxonomic revision of the basal neornithischian taxa Thescelosaurus and Bugenasaura", Journal of Vertebrate Paleontology, 29 (3): 758–770, Bibcode:2009JVPal..29..758B, doi:10.1671/039.029.0328 Longrich, N (2008), "A new, large ornithomimid from the Cretaceous Dinosaur Park Formation of Alberta, Canada: Implications for the study of dissociated dinosaur remains", Palaeontology, 54 (1): 983–996, Bibcode:2008Palgy..51..983L, doi:10.1111/j.1475-4983.2008.00791.x Manning, P.L.; Ott, C.; Falkingham, P.L. (2008), "The first tyrannosaurid track from the Hell Creek Formation (Late Cretaceous), Montana, U.S.A", PALAIOS, 23 (10): 645–647, Bibcode:2008Palai..23..645M, doi:10.2110/palo.2008.p08-030r Bibcode:2008Palai..23..645M Bakker, R.T.; Sullivan, R.M.; Porter, V.; Larson, P.; Saulsbury, S.J. (2006), "Dracorex hogwartsia, n. gen., n. sp., a spiked, flat-headed pachycephalosaurid dinosaur from the Upper Cretaceous Hell Creek Formation of South Dakota in Lucas, S. G. and Sullivan, R. M., eds., Late Cretaceous vertebrates from the Western Interior" (PDF), New Mexico Museum of Natural History and Science Bulletin, 35: 331–354, archived from the original (PDF) on 2011-07-17 Henderson, M.D.; Peterson, J.E. (2006), "An azhdarchid pterosaur cervical vertebra from the Hell Creek Formation (Maastrichtian) of southeastern Montana" (PDF), Journal of Vertebrate Paleontology, 26 (1): 192–195, doi:10.1671/0272-4634(2006)26[192:AAPCVF]2.0.CO;2, JSTOR 4524549, S2CID 130751879 Weishampel, David B.; Dodson, Peter; Osmólska, Halszka (2004), The Dinosauria, 2nd edition, Berkeley: University of California Press, pp. 1–880, ISBN 0-520-24209-2, retrieved 2019-02-21{{citation}}: CS1 maint: publisher location (link) Pearson, D.A.; Schaefer, T.; Johnson, K.R.; Nichols, D.J.; Hunter, J.P. (2002), "The Hell Creek Formation and the Cretaceous-Tertiary boundary in the northern Great Plains: An integrated continental record of the end of the Cretaceous", Vertebrate Biostratigraphy of the Hell Creek Formation in Southwestern North Dakota and Northwestern South Dakota, Geological Society of America, vol. Special Paper 361, pp. 145–167, ISBN 978-0-8137-2361-7, retrieved 2019-03-22 Varricchio, D.J (2001), Late Cretaceous oviraptorosaur (Theropoda) dinosaurs from Montana, D. H. Tanke and K. Carpenter (eds.), Mesozoic Vertebrate Life. Indiana University Press, Indianapolis, Indiana, pp. 42–57 Currie, P.J.; Padian, K. (1997), The Encyclopedia of Dinosaurs, Academic Press, pp. 1–901, ISBN 978-0-122-26810-6, retrieved 2020-03-30 Eberth, D.A. (1997). Edmonton Group. San Diego: Academic Press. pp. 199–204. ISBN 978-0-122-26810-6. Lofgren, D.F. (1997). Hell Creek Formation. San Diego: Academic Press. pp. 302–303. ISBN 978-0-122-26810-6. Breithaupt, B.H (1997). Lance Formation. San Diego: Academic Press. pp. 394–395. ISBN 978-0-122-26810-6. Christophel, D.C. (1976), "Fossil floras from the Smoky Tower locality, Alberta, Canada", Palaeontographica, Abt. B, 157 Chandrasekharam, A. (1974), "Megafossil flora from the Genesee locality, Alberta, Canada", Palaeontographica, Abt. A, 174 Estes, R.; Berberian, P. (1970), "Paleoecology of a late Cretaceous vertebrate community from Montana", Breviora, 343: 1
External links Cretaceous Hell Creek Faunal Facies provides a faunal list Phillip Bigelow, "Hell Creek life: Fossil Flora & Fauna, a Paleoecosystem" Paleobiology Database: MPM locality 3850 (Hell Creek Formation): Maastrichtian, Montana